1. Field of the Invention
The present invention relates to a nozzle tip for a pipetting apparatus, and in particular to an improvement of the shape of the nozzle tip.
2. Description of the Prior Art
In a pipetting apparatus, a nozzle is constructed from a nozzle base of the pipetting apparatus and a nozzle tip removably attached to the nozzle base. This nozzle is used to aspirate and dispense a liquid such as a reagent or a sample or the like. The used nozzle tip is discarded as required, and then a new nozzle is attached to the nozzle base. Normally, the nozzle tip is manufactured as an integrally formed product made of a resin.
An example of a prior art nozzle tip is shown in FIG. 3. In this example, a nozzle tip 10 is constructed from a head portion 12, a cylindrical portion 14, a step portion 16 and a tip portion 18. The head portion 12 has an opening 12A adapted to fit onto a nozzle base 8 of a pipetting apparatus (not shown in the drawing), and has a shape having a diameter larger than the diameter of the cylindrical portion 14. The cylindrical portion 14 has a roughly straight shape, but strictly speaking there is some tapering. The tip portion 18 is formed with a tip opening (small hole) 18A from which a liquid is aspirated or dispensed, and has a tapered shape. The cylindrical portion 14 has a lower end portion 14A having a larger diameter than the diameter of an upper end portion 18B of the tip portion 18, so that a step is created at the connecting portion therebetween with having a somewhat round surface. Namely, a step portion 16 in the form of a chin-shaped projection is formed between the lower end portion 14A of the cylindrical portion 14 and the upper end portion 18B of the tip portion 18.
However, in the case where the above-described prior art nozzle tip 10 is used, when there is a relative positioning misalignment between the nozzle tip 10 and a target container 20 at the time the nozzle tip 10 is inserted into the target container 20, there is the possibility that the step portion 16, namely, the chin-shaped projection will make contact with or become stuck on a part of a peripheral edge of an upper opening 20A of the target container 20. In such a case, since the peripheral surface of the step portion 16 forms a relatively steep inclined surface with respect to the central axis of the nozzle, there is the problem that it becomes difficult to smoothly insert the cylindrical portion 14 inside the target container 20. This problem can also occur in the same manner in the case when unused nozzle tips are set in a nozzle rack. In addition to the above problems since the tip portion 18 of the nozzle tip 10 generally has a thin thickness, there is a demand that such a portion of the nozzle tip 10 should be structurally reinforced.